Magmas and sulphide ores [Sudbury, Ont., deposits]

Arthur Philemon Coleman
1917 Economic Geology and The Bulletin of the Society of Economic Geologists  
Oxygen and sulphur seem to play a somewhat similar part in their com•oinations with the metals, and compounds of both occur associated with eruptive rocks in ways which suggest that they were originally included in the molten magma; yet certain geologists make a wide distinction between oxides and sulphides in their interpretation of the field relations of these two types of ores. .Every one accepts the r61e of oxides as highly :basic p.ortions of magmas which may be segregated when coolin,g
more » ... ed when coolin,g takes place. No one disputes that the titanife.rous magnetites and ilmenites associated with gabbros and anorthosites have been parts .of the fluid magma from which these rocks were fo.rmed; and yet protests are raised against a similar interpretat. ion of sulphides or iron, copper and nickel associated. with pyroxenites, d, unites and norites. The separation of oxide ore bodies from a basic, or even somewhat acid magma, as .in the case of the Kiruna magnetites, seems to arouse no hostility; •but in some minds the suggestion that the Sudbury sulphide deposits have segregated from the norite with which they are everywhere connected seems to be instinctively objected to as if it were contrary to the laws of nature. Th,is prejudice against the magmatic origin of sulphide ore deposits is the more surprising when one recalls that the source of the sulphides themselves is always sought in eruptive rocks. For example, we are astonished that the zinc and lead sulphide ores of Missouri cannot be traced certainly and directly to some mass of eruptive. Even if we incl.ine to account for them as derived f,rom marine rocks, we assume that the sea obtained its sulph•/tes from the leaching of former eruptive rocks. The great majority of metallic ores can be traced with certainty through the action of circulating waters to a source in some cooling eruptive 427
doi:10.2113/gsecongeo.12.5.427 fatcat:q4un3w2e5rc2royhkhfzxwtx5u